1. Field of the Invention
The present invention relates to an optical scanning device used as an optical system for writing, and an image forming apparatus, such as a printer, a facsimile machine and a copier, provided with the optical scanning device.
2. Description of the Related Art
An optical scanning device in which a polygon mirror is rotated with a motor and a laser light beam is irradiated to polygonal reflective surfaces of the polygon mirror for scanning is used in an image forming apparatus such as a copier and a laser printer.
When such optical scanning device is mounted in an image forming apparatus, a deviation of a main scanning direction of the laser light beam irradiated from the optical scanning device to a photoconductive drum is finely adjusted to ensure the perpendicularity of an image to the photoconductive drum. Conventionally, a folding mirror provided in the optical scanning device has been adjusted for such fine adjustment. However, especially in a color image forming apparatus, it has been necessary to adjust a plurality of folding mirrors in the optical scanning device for respective colors. Therefore, operations of assembling an image forming apparatus have been complicated and taking a long time, thereby causing a disadvantage in the aspect of manufacturing costs.
Therefore, various configurations to do easy correction of a deviation of a laser light-beam in an optical scanning device have been devised. For example, Japanese Patent Unexamined Publication No. 2004-170755 (D1) discloses a color image forming apparatus in which a deviation and distortion of an image bearing member is detected by using a detected registration misalignment for respective colors, and a laser light is irradiated at a timing and an exposure amount to correct the deviation and distortion and eliminate the registration misalignment.
Further, Japanese Patent Unexamined Publication No. 2001-242671 (D2) discloses an image forming apparatus in which each set of a photoconductive drum and a scanner of a plurality of imaging units is made in a pressed contact with a frame member to thereby accurately position the plurality of imaging units without performing any adjustment of the relative positional relationship therebetween.
However, the configuration disclosed in the D1 reference needs a detector for detecting a registration misalignment and a mechanism for adjusting the scanning timing and exposure amount of a laser light beam, consequently having a complicated control mechanism. Further, in the configuration disclosed in the D2 reference, the positional relationship between the photoconductive drum and the scanner is dependent on the accuracy in dimensions of the frame member, thus causing a problem that the positional relationship adjustment cannot be accomplished when the frame member is deformed.